Rotary compressor



June 1, 1965 R. E. LAMBERTON r-:TAL 3,186,630

ROTARY COMPRESSOR Filed Sept. 5, 21963 3 Sheets-Sheet 1 NR @E RWM E, OEWDA N F T En mm mMoRa m, f VA/ T um r I m/ RAR T Ew :E: EETM A um Bv Si nw Mummy LVBM MW ,GV MN A .L F N E W o 8.252 m25 YNY vu. NN l .mmh-, BME 2 m25 A m25 Em.. #5m M mmammm .wm .2. L r v ao.. o ...9: E@ N`k A Nmuv Nw Nv Q.\ V om P :zoo mm\ t.\ x Q mos/duw \w\/ S mv .Q DE uw w f A NTC. QM. hm.

F @T 4 w n G E a June 1, 1965 R. E. LAMBERTON ETAI. 3,185,630

ROTARY COMPRESSOR Filed sept. 5, 196s "':s sheets-sheet 2 l) 'n om cRc lons

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CL3 ZCRI B5 CLL TO RALPH m8 T N ORV/LLE R. LOWTH R BY ROBERTA. REDD/NG MAHg/VEY, MILLER RAMBO ATmR/VEYS June 1 1965 R. E. LAMBERTON ETAL 3,186,630'

ROTARY COMPRESSOR Filed Sept. 5, 1963 3 Sheets-Sheet 3 VENT RS RALPH .LAMBRT N F/ 3 ORV/LL R LOW HE ROBERT A. REDD//VG BY MHONEY MILLER a RA 0 5%@ f M A TT ORNE YS 3,186,630; ,y normar cowrrnnsson 1 Ralph Ei Lamberto@ 'Worthingtom land Orville' j -..ILowther V'and Robert A. Redding, Columbus, Gino,

assignors to TheJaeger yMachine Company, Columbus, Ohio,a corporation .ofOhio f v Filed Sept. 5, 1963,`Ser No.'306,952.1v f 13 Claims. (CL 23m-26) mpressor Awhile itis runninginan vunloaded -stat'e vis ment type'. Itl isv applicable, particularly, .to a rotary Vcornpressor of this general type which is driven by an electric motor although itis not ynecessarily limited to an electrically-driven compressor.l

f'jiOurV invention*relates toa rotary compressor. It .de"als,

more -specitically,.withan unloading system for apr-votary lcompressor whereby the powei` required to drive the' ftthe compressorlasrwell .as loading and'unloa'rling of the compressoriin .accordance with our invention.

A Vveatly reducedV as compared .to power3 requirements of prior .farteornpressors in a similar state:v t. M This invention deals mainly with compressors of the internally oil-cooled, sliding-vane rotor, positive-displace- At the present time, compressors of the general type 'u indicated are provided With-,unloading systems but by .l ,these systems only the intake valve of thecompressor is closed so thatatmospheric air -tobe compressed will not .be-taken Iinto the compressor and a very high .vacuum will y `result at theintake `side ofthe compressor unit. .The

rotor continues to rotate in the` unloaded state. of the '-compressor, even if there is no need to compress air., to provide for proper circulation ofthe relatively large Vol- Vume of lubricating-cooling oilfin the system. kHowever,

even in the unloaded state, therotor isrworking against the pressure in the air receiver whichis reected-back v y to the discharge chamber of the high-pressurecyiinder. "Sincel no airyis entering the low-pressure cylinder, vall vsectorsof both rotors bounded'by thelsliding vanes are' operating at a partial vacuum. As eachvsector of the khigh-pressure rotor is exposed to this receiver backpresf sure, 'air expands intothis cavity and must be recom- 4 pressed back to a pressure slightly greater than that of ythe receiver, as the rotor vanes -pass the discharge port. t

This alternate expansion and recompression results in a high power consumption for driving thefrotor in the unloaded state of the compressor as compared to the power i consumption required to drive it in theloaded state of the compressor,- ordinarily amounting to about 75% ofv the energy required to drive it in the loaded state. This is particularly true of the electrically-driven compressors, in which the electric motor drives at constant speed. Even in connection with rotary compressorsdriven by internal combustion engines, where the throttle is moved vto a minimum speed position during the time the compressor is unloaded, a substantial amount of power'and,

therefore, fuel is required .todrive the rotor while the compressor is unloaded.

It is the main object of this invention to provide an unloading system for a compressor of the type indicated 'which may be termed a-free unloading system inthatl the rotor will not be required to Work against the presgsure of -the compressed` air in the receiver part yof the `compressor unit and, therefore, the amount of power required to drive the rotor during that unloaded state will be ak minimum.

r' kAnother object .of y,our invention lis to provide a free- `,unload-ingv system of the type indicated in an internally, oil- 10 lVariousother In FIGURE l, we. indicate acompressor A `further object ,of our invention is'totprovi'dea freek'unloading', systeme-,ofthe multi-stage type wherein an yinterstage.manifoldconnects the stages of the compressorl having ya-n.oilascavenging'system associated therewith for preventingthe accumulation ,of excessive amounts of oil in ythe manifold while thecompressor iis operating in the unloaded state.

AVtion progresses.- r

In t-heiiccompanying drawings, we haveillustratedone 1 embodiment of ourl invention, the embodiment shown being `a ,compressor zwhich is electricallyv driven, Vbut it is to be understood that manyfspeciiic variations are possible withoutrdepart-ing from basic ,princip'les fof jour in- Y vention.

In these drawings: f I FIGURElis a `schematic diagram of the tiuidsystemv of .a rotary compressor y,'er'nbodying ourjinvention with certain electrical member-s`ir'1dicated 'in association there- FIGURE 2 isasch'ematic diagram of thelelectrical sys- I tem ,used onthe:compressor in accordance with our invention.y

e FIGURE 13, is scavenging :system ,associated with the free-unloading system. y f

With referencetodhe drawings, in-FIGURE 1 we have illustrated schematically va rotary compressor system to which our inventionis applicable, but it is to be understood that weare notl limited tothis specific compressor system. The structure of the'rotarycompressor itself may ybegenerally like Ythat disclosed in the patent to Lamberton as l shown herein asbein'g an electric motor. The'general No. 2,739,758 .issued Marea 27, V1956,1mt its driven arrangement andpositioning of, 'the various units of the compressor system may be similar to that disclosed in the copending `application of PaughSer. No. 215,390, ltiled( August 7, r19,62, nowU.S. Patent`3,l56,409f

1t) of the 'rotary V typewhich is dri-ven by an electric motor indicated at 1i. The compressor maybe of the multi-stage type -and is tshown as having a low-'pressure kcylinder 12 and a high-pressure'cylinder 13. These cylinders are connected together Abyk an interstage manifold 14 so that low-pressure air discharged from the cylinder 12wil1 be conducted into the cylinder 13 for `further compression.v The lowpressure cylinder i2 houses a rotor (not shown) preferably ofthe sliding vane type which is coupled to and is driven by the motor 11. The rotor` in the low-pressure v cylinder kis coupled to and drives the rotor (not shown) which is in the Yhigh-pressure cylinder 13. The low-pressure cylinder l2 is provided with an air intake conduit 1S having a two-way unloading valve 1 5 connected therein Vwhich is of the piston type and is adapted to be actuated n by air-pressure. A lter 17 is also provided for the intake conduit 15 so that air taken into thevlow-pressure cooled compressor wherein an unloading point is selected :j

l in the `system where 'the airis s ufticiently free ofl circulat- Ying lubricating-cooling oil toallow it to be exhausted tothe atmosphere without excessive loss of oil.

Another robject of our invention -is to provide a control .system `for a vcompressor of the type indicated which preferably will automatically control starting and stopping cylinder l2 from 'the atmosphere vwill beofltered. Also connected to the lter `17 is an air `conduit 16 which is adapted to'inspirate air into the interstage manifold i4,

vto the low-pressure endlof which itis connected as shown.

This'conduitl is provided with the check valve i9.v The conduit 18 -functions ina manner, to bedescribed in dei'fal laelsfto aid in Preventing undue accumulation fof oil 'inthe manifold 14..

' The V11igit-pressure kcylinder 1s is provided with im'4 utlet ordischargechamberffortthe compressed'airand oil mixture which connects by a discharge'conduit 20 to the receiver tank, indicated at 21, and a check valve 22 is lprovided in this conduit. ,A ythermally-actuated electric switch THl is'also associated with the discharge conduit 'tassista Patentedgune 3.,1955

objects will be apparent as this deseripaiView:illustratingY details of the oili beyond the .check-valve 26,;

' an exhaustA silencer S0 of a suitable type.

sure fcylinderln Anoil' reservoir tank is illustrated at` .i

i' -23 below the receiver tank 21. and connected thereto.

An air-oil Vseparator,v is indicated at",2;4"'above the tank-21.1215

and i, s'connected thereto. The separator'Z-t'is connected,l

i to the air-service conduitZS .which hasa check valve i therein and which st xliplies the air compressed by the corn-Y controlled .byv their respeccorpora'ted ineach magnetic contactor are the Yusual over,-

load.gprotectiveV devices consisting lof the.r associated thermally-responsive elementsand ynormally closed contacts CLL CL2', VOL3 and OMIA.V lAs Will' be lnoted from `the circuit diagram, themverload devices OLlj andl OLZ pressor to the pointdof use. An.oil bleeder'conduit 27.`

providedwith a Vstrainer 28 :and a check valve 29, associl leads ro'rnthe lower portion of the separator'24andA con-v g nects to the low-pressure end' ofr the manifold 1li-,being i the desired voltage for operation ofthe control -circuit. v 2.', The controllcircuit includes: a Ystarrt-stop. circuit having ated with a restricted passage to the manifold, zconnected therein in series. This conduit' 27ffunctionsftoreturn the;

separated oilto the interstage manifold 14 .a

does it in a manner to 'aidin scavenging oilfrom the manifold asfwill be described Vin detail later; g v Oil for lubrication and cooling is rotor in thecylinder 13'. Thedischarge'of this pumpjis l Supplied` Byarumn l 3inthe usual'nianner,rthis pump beingfcoupled to the x connectedby an oil conduit 31 to theoil supplysystem of the cylinders 12 and-13 which. is indicated schematically as stead-of this flow switchZlT-heinlet side'ofthefpump 30is' Vjthe'gallery 32 and a ow switch FLS is interposed Yin thisV oil conduit 3E although a'pressure switch may Ibefused infv.connected by an oil conduit 33 to an oil cooler indicatedat Manda iilterSS is,interposedfin.thisV conduit. Also`,'- a' i thermally-actuated switch THZis associated `with this con--V 'l duit and is :actuated by the temperature ofthe oiltherein from the cooler 34'.VU A blower isindicated `at 36aspart ofthe oil-'cooler and is driven by an velectric motor 37. An

.oilconduit 38 leads `fromthe .oil reservoir 23 tothe oil i cooler'Sft-fthrough'a thermally-actuated by-pass Vvalve Y40 which Yis" actuatedfbythetemperature of the oil 'coming g5 from the tank ,23; j A by-pass oil vconduit 39 is alsocon-` leading from the oil cooler 34.

The` pressure-actuated unloading Y nected to this valve 40 and connectsrto the oil Vvconduit33 valve lois connected by ranvair .conduit 41`to -al three-way solenoid actuated "l valve S2 is -an air conduit 44 whichconnects to an air `con-` actuated electrical switch'fPS is connected togthe conduit duit 45 Vthrough anair-liquid separator 46. A pressurel45 and this conduit ,connects to the air service conduit 25 The unloading `system according to our inventionalso and L35,

'motor 37.'.Also connected tof the power linesLl and L3 is a lcontrol circuit-voltage "transformer 57'fwhich provides manually-actuated startgandrstop swiEchesSS and -59 VwhichV rnay'fjbe'of theYpushbuttonftype..l The stopjswitch'59 is normally closed while the startswitch' is normally. open with -the.'contacts ofeachbeing serially" connected acrossr the .secondary outputsconductors ofjthe transformer7;` `Also 'connected in series with the Vswitches 578 'and 59 is the coil 3CRjof la' circuit-.maintainingrelay which" by-passes 'the' start switch `58.',Qoncevtth'e compressor,- apparatus'has been ystarted and is operating normallyf` i Completion of the start and stop circuitV isthroughga serially-connected, thermostatically-operated switch Tl-11,* V.previously mentioned, and the; normallyclosed contacts of the overload ,'*devi-ces. OLI and '.OLZ uassociated. with the compressor t motor 111i. r 'The thermostatic switch THll isf provided with Y a normallyrclosed lcontact which Vwill openl when the ternlperature of` the. oil-air mixture discharged from the high- A' pressure staged?,v of the compressor Vexceeds'at predeter- Y mined value; In this'presentembodiment, Vthe switch THl f is set to open at about 240 Rand will break they startstop circuit, .thusV protecting the'jcomp-ressor apparatus Y,

fromjda'mage' due to high'temperatures. Seria-llyconnecting the contacts of the overload `devices OLI and OLZ in thestart-stop circuity provides'further protection for the compres-sor apparatus in the even-tthat an overload should occur inthe 'compressor motor 121.. An overload of this f form would also bre-akkthelstart-stopgcircuit deen'ergizing the control circuit and ,disconnecting `the compressory and blower motors 11 and 317' from thepower lines L1, L2

A holding `circuit is connected in'V shunt relationship with the start switch 58' which automatic-ally operates to deincludes an exhaust valvev S1 Which is connectedto'the oil f sepa'rator'Z. by a conduitSl.` This'valve Slis a solenoidactuated two-wayvalve. Its exhaust side is connected to An electricalupowerand control circuit for operation of the compressor in accordance ywith this invention is dia-i grammatically illustrated Vin FIGURE 2.` The'controlicircuit, YasV illustrated,'is adapted to not only automatically control operation of the compressoras toloadedrand unloaded operation in accordance with service kdernandsi'but erate the several components fof the apparatus as to provide for free-,unloaded operation of the compressor;

' rThe 4electrical power circuit is connected to a lthreephase,.alternating,ir current power distribution systemof andL. vAV three-pole disconnect switch 55 is interposed power lines L1, LZand L3 are the electricjmo't-ors 37 'and 'in the powerlines along fwith Lthe necessary overcurrent Y -pr-otective devices-'sueltas the fuses 56,1 Connected to the 'I i Arelay; The connec'tionA ofY the operating coil-s'lCR and tactsV of the iiow switch `FLS `:are normally open.

to automatically start and stop the apparatus in accordance 4with predetermined operationaly conditions. It is the pri- `maryfunction .of the control circuit to automatically opsuitable voltage and includes theVv three power lines L1, L2

energize the-control circuit and disconnect vtheY .compressor and blower motors,` lland 37. 'I'hisci-rcuit includes the nected contactslTRl 'of a time delayrelayV and the flow `switch VPLS previously. mentioned."` The vcontacts lTRl of the timedeiay relay are normally closed while the con- As previously indicated, the'flow. switch PLS is interposedrin ,thedi-scharge conduit 31 of theioil pump `3i) and is respone ing coils vICR and ZCR fortthe magnetic motor contactera Each coil, ICR and ZCR, isv connected in Yseries with its respective serially-connected overload contacts, OLI and OLZ," OLS and CL4.. Thel coils VICR and ZCR with their respective overload'V contacts are connected inshunt rela- -tionship Vand may be connected to the` holding Ycircuit jthr-ougheith'er a manually-actuated'selector switch 60 or through the normally closed contacts 2TR1 of a ,time delay ZCR to theholdingicircuit is'made Vat the juncture of the parallel -connected timercontacts1TR1 and.flow switch Ycontact FLS whereby the relay contacts SCR-1 will be etreetive to` control the operation ofthe blower and compressor motors .11 and 37. The selector switch 60 is of the two-y position type and is adapted to complete the circuit to the Operating coils 1CR and ZCR in a first position and is open-circuited in the second. -As will be noted from the circuit diagram, the selector switch 60 is connected in shunt relationship to the ltimer contacts 2TR1 and is etfective to by-pass these contacts when in .the first position. Interposed in the circuit of the operating coil 2CR .are the contacts of the thermal switch TH2 previously mentioned. These contacts are of the normally-open type with the switch being set to close the contacts at about 120 F. and to open the contacts at about 110 F. The thermally-responsive element of the switch is installed in the Oil cooler outlet conduit 33 and is effective to maintain the temperature of the oil within predetermined limits by cont-rolling the Operation of the oil cooler blower m-otor 37.

Also connected in shunt relationship to the operating coils 1CR and 2CR is the operating coil TR of the time delay relay. This relay is of the type Kwherein the contact action is retarded upon energization of the operating coil. In the `present compressor system it has been determined that a del-ay of about l seconds time in opening of the contacts 1TR1 `is desirable for optimum operation of the system. At any time the coil '1TB is deenergized, the coil and contacts 1TR1 will be instantaneously reset to their normal position.

An automatic free-unloading circuit is provided by this invention to simultaneously open the compressor high- `pressure stage `discharge to the atmosphere, by opening the valve S1 previously mentioned, `and to close the unloader valve 16 preventing `further intake of air. The free unloading circu'it includes the solenoid-actuated valves S1 Iand S2. Selective energization of the solenoids of the valves S1 and S2 is effected through a pressure switch PS. This switch is responsive to the pressure in the air service conduit 25, through the connected conduit 45, and is of the single pole, double-throw type. In the first or low-pressure position, the pressure switch PS, the pole of which is Ialso connected to the holding circuit so as to be in series with the relay contacts 3CR1, completes a circuit thro-ugh the solenoid of the valve S1. In the second or highpressure position, a circuit will be completed through the Solenoid of the valve S2. The operating pressure limits of `the switch PS, in the present embodiment, are set to maintain ra circuit through the solenoid of the valve S1 at any time the pressure in the fair service conduit 2S drops below 90 psig. land to maintain a circuit through the solenoid of the valve S2 at any 4time the pressure in the air service conduit reaches 105 p.s.i.g.

Connected in parallel with the solenoid of the valve S2 is the operating coil ZTR of the second time-delay relay. This relay is operative to effect automatic start and stop of the compressor and blower motors 11 and 37 in accordance with the air pressure in the air service conduit 25. This relay is also of the type wherein the Contact action is retarded upon energization of the operating coil. Since the coil 2TR is connected in parallel with the solenoid of the valve S2, it will be energized simultaneously therewith when the air service conduit pressure reaches 105 p.s.i.g. The contacts 2TR1 will not open, however, until the time delay of the relay has elapsed. At the eX- piration of the time delay, the contacts 2TR1 will open and deenergize the operating coils 1CR and ZCR causing the blower and compressor motors 11 and 37 to stop. The delay, which may be of the order of l5 minutes, has been found advisable in order that the number of starts will be limited to four in any one-hour time interval. This is necessary to prevent overheating of the compressor motor 11 due to the relatively large starting current. When the air service conduit pressure drops to 90 p.s.i.g. and deenergizes the solenoid of the valve S2, the timer coil ZTR will also be deenergized and'will be reset in preparation for another timing interval. Simultaneously, with reset- Y ting of the operating coil ZTR, the contacts 2TR1 will 6 close permitting restarting ofthe compressor and blower motors 11 and 37.

As previously indicated, the conduit 18 is part of an oil scavenging system according to our invention which prevents the accumulation of oil in the manifold 14 during the unloaded operation of the compressor 1t). This sys.

' tem is shown more in detail in FIGURE 3 and functions during the time the compressor is operating in the freely unloaded state. This scavenging system is an air-inspirating system which is connected to the manifold 14 and which operates on a pressure differential between the manifold and atmospheric air at the compressor intake to draw air from the atmosphere, during the unloaded cycle and to jet it through the manifold in the direction of normal iicw through the manifold and thereby to scavenge the oil therefrom.

The bleed or drain conduit 27 running from the oil separator 24 also functions as a scavenging system during the unloaded operation of the compressor, as previously indicated. It also produces a jet of fluid through the manifold to prevent accumulation of oil therein.

The compressor air inlet is controlled by the valve 16 which may be a common type of unloading valve, an example of which is illustrated in FIGURE 3. It comprises a piston type valve member 66 which is actuated by receiver pressure reaching it through the conduit 41 controlled by the valve S2 previously mentioned. This valve member 66 is disposed in a housing 6s mounted on the low-pressure cylinder 12 over its inlet 1S and cornmunicating therewith. The housing is provided with an inlet sleeve 7i) leading thereinto having a valve seat 69 at its'rinner end with which the valve member 66v cooperates. On the outer end of the inlet sleeve 70, the filter unit 17 is mounted. Atmospheric air will be drawn through the filter unit 17 and be filtered before it enters the housing 68 through the inlet sleeve 70.

During the normal operation of the compressor, the oil passing from the low-pressure cylinder 12 with the air will pass into the high-pressure cylinder 13 and out to the air receiver 21. During both the loaded and unloaded states of the compressor, the interstage manifold 14 will be at a much lower pressure than the oil separator 24.

While the compressor is loaded, the oil passing from the low-pressure cylinder 12 with the air will pass into the high-pressure cylinder 13 and out to the air receiver 21. The compressed air flows from the receiver 21 into the separator 24 and any oil vapors remaining in the air are retained in the filtering elements in the oil separator and are passed fromthe separator into the drain or bleed line 27. The check valve 29 in the conduit 27'will prevent oil from being forced back up into the separator when the compressor is started. As soon, after starting of the compressor, as air pressure in the discharge end of the oil separator 24 exceeds the pressure in the manifold 14, any oil collected by the oil separator 24 will be forced into the manifold 1d. The main stream of oil and air, as indicated, during loaded operation of the compressor will flow through the manifold 14 and there will be no tendency for oil to accumulate therein at this time. The oil and air returned from the separator 2d by the conduit 27 will merely be added to that mainstream. However, the connection ofthe conduit 27 to the interstage manifold 14 according to our invention, will prevent the accumulation of oil in the manifold when the compressor is running unloaded. When the compressor is running unloaded, there is a tendency for oil to accumulate in the manifold since there is very little air in circulation within the compressor at this time, due to the fact that the unloading valve 16 is closed, and the oil flow into the compressor is maintained by the oil pump 30. It will be noted from the drawings that the conduit 27 is connected to the upstream end of the manifold preferably directly over the bottom wall thereof, as shown best in FIGURE 3, to direct the oil iow parallel to the bottom wall.

Without our scavenging system, if the compressor runs `of the high-pressure rotor.

vacuum. Vpressure differential, from the separatorfto the manifold. Thus, there isA a jet of uid created and directed throughV Should turning the compressortoV loaded operation, the accumu- -lated oil will instantly `bedrawn into the high-pressure cylinder 13 and, if a suiciently large volume of oil has accumulated, causes a hydraulic jam between the vanes I Such an accumulation of oil could damage or distort the vanes. Also, if the air compressor is a portable compressor and is used for work on very irregular terrain, the compressor may be opeating` at vey steep angles which could possibly cause an excessive accumulation of oil in the lowest end of the manifold with resulting serious damage or breakage of the vanes of the rotor in the high-pressure cylinder. the conduit, runningfrom the separator 24, connected to the upstream end of the manifold'ld, the oil and air mixture from the separator will be injected into the manifold toward the downstream end thereof. As will later appear, during the unloaded state of the compressor, the separator 24 will also be unloaded or connected Yto the atmosphere vWhereas the manifold will be at a lower pressure or Therefore, air and oil will flow, because of this ItheV interstage manifold 14 fromthe upstream end to its downstream end which is the normal direction of flow `of the main stream of air and oil mixture, from the lowpressure `cylinder 12 to the high-pressure cylinder 13. However, since during theunloaded state of the compressor there is no substantial ow of air throughtheV as another means to prevent accumulation of oil inthe interstage manifold 14 during the peirods when the compressor is unloaded. This conduit 18 constitutes -a piping system, between the interstage manifoldrand the air intake ofthe compressor, which provides for the inspiration of air through the intake filter 17 to the manifold 14 to produce a jet therein which will aid in forcing the oil from the manifold into the high-pressure cylinder 13. For this purpose, we connect the'conduit 18 at one end to the unloading valve unit 16 and at its other end to the upstream end of the manifold 14. Thus, the inlet end 72 ofthe conduit 18, as shown in FIGURE 3, is connected to the valve unit 16 at the inlet sleeve 70 at a point intermediate the lter 17 and the valve seat 69. The air taken into the conduit 18 will, therefore, be filtered air. The other or outlet end 73 of the conduit is connected to the *manifold- 14 at its upstream end and directly above the bottom of the manifold adjacent the point lwhere the outlet end 7dof the bleeder pipe or conduit 27 is also connected. The outlet ends 73 and 74 of the conduits 18 and 27 Iare directed toward the opposite or downstream end of the manifold 14. The conduit 18 is provided With a check Vvalve 19 previously mentioned which closes when sufficient positive pressure'develops in the manifold 14 to preto the inlet of thekunloader `not for the provision of ourscavenging system, there could be a rapid buildup of oil in the'interstagemanifold 14. Since at this time the manifold 14 is under high vacuum, there is a substantial pressure differential between However, withy `the manifold and the compressor filter 17 which communicates Vwith. the atmosphere,` it being understood that the unloading Vvalve 16 is closed at this'time. Also, at this time, as will later appear, the. pressure side of the cornpressor is unloaded and there is no substantial pressure in the receiver 21 or ythe separator 2d.V The pressure differential between atmospheric air at the inlet and the low pressure in the manifold 14 is utilized, according to our invention, to inspire atmospheric air into said manifold and use it as a scavenger jet to act in a downstream direction on any oil tending tofaccumulate therein and to cause the 4oil to flow toward and into the high-pressure cylinder13.

Thus, .with this arrangement, since the unloader valve 15 is totally closed when the compressoris running in an unloaded state, Yair will be inspired from the chamber in the sleeve 7) between the valve seat 69 and the intake intake.

load, the valve 16 is opened by atmospheric pressure sincey filter 17'. Consequently, only filtered air is drawn into the holding pressure has been exhausted from the conduit 41, a positive pressure develops in the manifold 14 and the check valve 19 is closed thereby preventing air and oil' flow-back through the conduit 18 into the compressor intake. Y

Thus, both the .conduit 27` from the oil separator Z4 and the conduit 18 from,l the unloader valve'16 will function, during the unloaded state .of the compressor, to

create jets of Huid injectedV at the downstream end of the manifold 14 and directed toward the upstream end thereof in the direction of normal flow therethrough. These jets will scavenge from the manifold any oil which tends to Vaccumulate therein during the unloaded operation of the compressor.

The operation of the oil-scavenging system ofthis invention has been described above in detail. This system will function Whenever the compressor is4 operating unloaded.

The general operation of the compressor and especially as it relates to the free-unloading operation is brieiiy described herein as `related to the schematic` diagrams of FIGURES 1 and 2. In these diagrams, the several elements or components are shown in their normal positions as when the compressor systemris not operating. In this condition, the disconnect switch will be open and the pressure in the air service conduit 25 kmay be at atmospheric pressure or at least below the minimum 'desired operational pressure of theV system. The-exhaust .valve S1 will be open since its solenoid will be deenergized. Also, the solenoid of the control Valve S2, which is deenergized, will be positioned as shown to exhaust orlvent the conduit 41 to the atmosphere. The unloader valve 16 will thus be in its normally open position as-the actuating air cylinder is not pressurized; Since the temperature of the-lubricating and cooling oil in the system will be below -the minimum desired forl operation, the thermal by-pass Yposition Vdenoted ACONT. RUN will eliminate the automatic start-stop features of the system but not the freeunloading operation.

Initial starting of the compressor system is preceded by closing the disconnect switch 55 which will energize the control circuit transformer 57 and the control circuit connected thereto andalso connect the contactors of the com- 9 Y pressor motor 11 and the blower motor 37 to the power source. Subsequent to closing of the disconnect switch S, the start switch 58 is momentarily depressed to complete the starting circut as has been previously described in detail and cause relay contacts 3CR1 to close. While the compressor motor 11 will be immediately started, the blower motor 37 will not start until the temperature of the oil in the system has risen to a desired maximum, 120 F. for example, causing switch THZ to close. A subsequent decrease in the oil temperature to a predetermined value, such as 110 F., will cause switch THZ to open and the temperature of the oil will be maintained within the desired limits.

Since the pressure in the air service conduit 25 at the time of initially starting will be below the minimum operational pressure, Which may be 90 p.s.i.g., switch PS will be maintained in its first position energizing the solenoid of the exhaust valve S1. When thus energized, valve S1 will be closed, preventing further ow of air through conduit 51, permitting a build-up of pressure in the air receiver 21 and connected tanks and conduits. Continued operation will permit the oil pump 3i? to induce an oil iiow through conduit 31 into the oil gallery 32 of the compressor 10. After establishment of a minimal oil flow, the ow lswitch FLS will be actuated closing its contacts and thus by-pass contacts 1TR1. The contacts 1TR1 will remain oy-passed as long as oil is tiowing through conduit 31 for proper cooling and lubrication of the compressor 10. Simultaneously with starting the compressor 11i, the operating coil ITR of the time delay relay will be energized and will open its associated contacts 1TR1 after a predetermined time interval of, for example, tive to ten seconds. Opening of the contacts ITRI places continued operation of the compressor system under control of the flow switch PLS. At any subsequent time, should the oil flow from the pump 36 be insuticient tor cooling and lubrication, the flow switch FLS will open to deenergize v relay coil 3CR causing contacts 3CR1 to open and thus disconnect the remainder of the control circuit from the transformer 57. y

Assuming that the compressor 1li and its oil pump 30 are operating normally, air will be drawn through the air-intake iilter 17 and the open unloader valve 16 into the low-pressure stage 12 of the compressor during a loaded operational cycle. The air will be compressed and discharged through the conduit Ztl intoV the air receiver 21 and other connected tanks and conduits toibuild up the compressed air supply. The contacts of the pressure switch PS will remain in the illustrated first position durving loaded operation of the compressor 111 for a continued supply of compressed air. A loaded operational cycle will continue as long as there is a continued demand for compressed air and the pressure in the air service conduit 25 does not reach the maximum operating pressure which may be about 105 p.s.i.g.

When the compressed air requirements have been fully met, or the capacity of the compressor is such that the output thereof exceeds the current requirements, the compressor system of this invention will automatically revert to free-unloaded operation to minimize power consumption. In the usual compressed air systems where the maximum desired operational pressure may be approximately 105 p.s,i.g., the pressure switch PS is set to be actuated at this maximum pressure and the pole thereof will be switched to the second position to energize the solenoid of valve S2. Simultaneously, the solenoid of valve S1 will be deenergized and this spring-biased valve will be opened thus venting the conduit 51 to the atmosphere through the exhaust silencer Sti, thereby venting the receiver 21 and associated tanks 23 and 24 which are the major elements of the compressor unit receiver system. Energizaion of the solenoid of valve SZ causes displacement of the movable member thereof to connect the conduit 44 to conduit 41. Pressurization of the air pilot actuator of the unloader valve 16 is thus effected as the pressure in conduit 41 will be that of the air service conduit 2S to which conduit 44 is connected and the air may flow freely through the check valve 42 into the air pilot actuator of the unloader valve 16. The unloader valve 16 will thus be closed preventing further flow of air into the low-pressure stage 12.

Free-unloaded operation of the compressor 10 with the unloader valve 16 closed and the high-pressure side of the compressor opened to the atmosphere through the air receiver 21, separator 24 and conduit 51 will continue until the pressure in the air Service conduit 25 has dropped to the minimal operating pressure of approximately p.s.i.g. At this pressure, the switch PS will be reset to its first position for further loaded operation, as previously y described. Valve S1 will accordingly be actuated to close conduit S1 and the control valve S2 will return to its normal position closing conduit 44 to the intake valve pilot actuator, venting conduit 4'1 to the atmosphere. The pressurized air Within the actuating cylinder of the unloader valve 16 will exhaust through the restricted bypass 43 and conduit 41 tothe atmosphere. The restricted by-pass 43 prevents instantaneous operation of the unloader valve 16 for protection ofthe valve and the compressor 10.

During this free-unloaded operation of the compressor, the scavenging system including both of the jets produced by the lines18 and 2'7, as previously described, and directed into the manifold 14 will function to prevent accumulation of oil in the manifold.

An automatic starting and stopping circuit is also ineorporated in the compressor system, as previously indicated. Duringfree-unloaded operation, the operating coil ZTR of the second time delay relay will be simultaneously energized with the solenoid of Valve S2. This time delay relay, which may have a delay of approximately 15 minutes in the actuation of its contacts :ZTRL will control the stopping of the compressor motor 11 and blower motor 37. The timing interval begins at the start of the free-unloaded cycle and the contacts 2TR1 will open at the expiration of this timing interval. Upon opening of contacts 2TR1, the operating coils 1CR and 2CR of the motor contactors and the operating coil 1TR of the first time delay relay will be disconnected from the circuit. Contacts 1TR1 will instantaneously close and the liow switch FLS will subsequently open when the oil flow through conduit 31 has suiiiciently decreased. At any subsequent time that the pressure in the air service conduit 25 decreases to 90 p.s.i.g., switch PS will be reset, deenergizing the solenoid of valve S2 and the operating coil ZTR of the time delay relay. Contacts 2TR1 of this relay will be instantaneously closed to reconnect coils 1CR and ZCR and 1TR into the circuit. The compressor motor 11 and blower motor 37 will thus be restarted, as previously described, in conjunction with the initial starting phase.

It will be apparent from the above that our invention provides in an internally oil-cooled, positive displacement type rotary compressor, means for greatly reducing the power `required to run the compressor in an unloaded state, that is, when it is not pumping a substantial volume of uid at an elevated pressure. The unloading of the intake side of the compressor is accomplished at the intake valve whereas the unloading of the pressure or receiverk side of the compressor is accomplished by venting the air therefrom at a point where the air is sufliciently free from oil to allow it to be exhausted to the atmosphere without a loss of circulating oil. Thus, the power to drive the rotors during the unloaded state of the compressor is greatly reduced. Furthermore, this invention provides oil scavenging means which functions in association with the unloading systemy for preventing the accumulation of oil in the interstage manifold which otherwise might cause damage to the rotors. The control system for the unloading and loading operations as Well as all other operations of the compressor are completely automatic.

thev number of startsv of the electric motors to prevent damage thereto. Y Y( j v- The oilg tank'23, the receiver 21 and the separator 24 are shown as separate tanks but it is to be understood that the oil could collect in the bottom of the receiver tank so that the separateY oil tank could be eliminated. 'Also,

the oil separator tank could be disposed within the receiver tank. Our free unloading system and the associated oil scavenging system would work equally as well with such modifications of the compressor system.

According to the provisions of the patent statutes, the principles-of this invention have been explained and have been illustrated and described in what is now considered to represent the best embodiment. v However, it is to be understood that, within the scope of the appended claims,

the invention may be practiced otherwise than as specifically illustrated and described.

Having thus described our invention, what we claim is:

1. A rotary compressor comprising low-pressure and high-pressure stages having Vair-compressing rotors, a pressure lubricating-cooling system for said stages and connected thereto for supplying oil thereto, an inlet valve controlling the inlet of air to be compressed into said low-pressure stage, an air and oil receiver system connected to ythe discharge of said high-pressure stagefor receiving the oil and air mixtureA discharged thereby, said `lreceiver system including separator means for separating the oil and air of the mixture, said separator means having an inlet for themixture, an outlet means for the air and an outlet means for the oil for returning it tov said stages, a venting unloading valve connected to said separator air outlet means of the receiver system, said receiver system including a service line leading therefrom and connected to said separator air outlet means thereof, a check'valve in the service line for preventing venting of said line upon opening of said venting unloading valve in the receiver system, -and control means connected to both of said valves for closing the inlet valve and opening the venting unloading valve to freely unload the compressor, saidl control means comprising a pressure line connected to said service line and to said inlet valve for'actuating it to close said inlet valve when pressure in the service line reaches a selected upper limit and thereby to unloadvthe inlet side of the compressor.

2. A rotary compressor according to claim 1 in which said receiver system venting valve is an electrically-actuated valve and said inlet valve is controlled by a second electrically-actuated valve, and an electric circuit connected to both of said electrically-actuated valvesl for simultaneously opening the venting valve and closing the inlet valve.

3. A rotary compressor according to claim 2 wherein keach of said valves includes an electromagnetic solenoidV for actuation thereof and said electric circuit includes a power source and switch means connected in circuit with said power source and said valve solenoids to control the operation of said valves, said switch means being of the 5. A rotary compressor according to claim 2 wherein saidr air-compressing rotors are provided with a drive motor and said electric circuit includes control apparatus Vfor'selectively starting or stopping said rotor drive motor, Vsaid control apparatus having an Yelectromagnetic solenoid operableon energizationthereof to start the said rotor `pressure-actuated type having a pressure-responsive elel2 drive motor and operable ,on .deenergirzation thereof to stop the Isaid rotor'dr-ive motor, and timer-'actuated switch means connected in said electric circuit to deenergize Vsaid Vcontrol apparatus solenoid at a predetermined` time subsequent tothe pressure in said service line reaching and being maintained at saidpredetermined high level for said predetermined time..` i Y 6. A rotary compressor according to claim 2 wherein said lubricating-cooling system includes a heat-exchanger havinga drive motor and said electric circuit includes means for selectively starting or stopping-said heat-exchanger drive motor, said means including thermal switch means responsive to the temperatur-eef the lubricatingcooling medium in said lubricating-cooling system.

7. A compressor according toclaim 1 in which the low-pressure stage is connected to the high-pressure stage by an interstage manifold,.andmeans forl scavenging oil from the manifold, said means comprisingra fluid line connected to said manifold at the upstream end thereof and connected to a source of uid under greater pressure than that in the manifold during the unloaded state of the compressor. Y

8.` VA compressor according to claim 1 in .which the lowpressnre stage is connected to the high-pressure stage by an interstage manifold, and means for scavenging oil from the manifold, said means comprising an air line connected to atmosphere when said inlet `valveis closed, and connected to said manifold at the upstream end thereof.

9. A compressor according to claim 1 in which the lowpressure stage is Vconnected to the high-pressure stage'by an interstage'manifold, said receiver system comprising a receivery tank and ran Oilseparator connected thereto, means for scavenging oil fromr the manifold, said means comprising a fluid line leading from the oil separator and being connected to said'manifold at the upstream end thereof.

14B. A compressor according to claim 6 in which the scavenging means also includes an air line connected to atmosphere when said inlet valve is closed and connected to said manifold at the upstream end thereof.

11. A rotary compressor having la fluid inlet system and a fluid receiver system with fluid-compressing means connected therebetween and having a discharge outlet, a pressure-lubricating-cooling system for said compressing means and connected thereto to supply lubricating and cooling oil thereto, said inlet system including unloading means for unloading the compressing means, said receiver system including Vseparator means which receives air and oil mixture discharged from said discharge ,outlet of said Vcompressing means for'separating the oil andV air of the mixture, said separator means having an inlet for the mixture, an outlet means for the air and an outlet means for the oil for returning it to said Vcompressing means, a venting unloading means connected to said separator air outlet means, and control means connected to both of said unloading means for actuating them simultaneously.

12. `Aerotary compressor Vhaving a iluid inlet system and a fluid receiver system with huid-compressing means connectedk therebetween and having a discharge outlet, a pressure-lubricating-cooling system for said compressing means and connected thereto to supply lubricating and cooling oil thereto, said inlet system including unloading `means for unloading the compressing means, said receiver system including a separator means which receives air and oil mixture discharged Afrom said discharge outlet of said compressing means for separating theY oil and air of the mixture, said separator means having an inlet for the mixture, an outlet means for the air and an outlet means for the oil for returning it to saidcompressing means, a receiver system venting unloading means connected to said separator airoutlet means','said receiver system including a service lline leading therefrom and connected to said separator air outlet means, a checkvalve in, theservice line for preventing venting of said line upon opening of said receiver system venting lunloading means, and conamasar vand a fluid receiver system with uid-compressing means connected therebetween and having a discharge outlet, a pressurelubricating-cooling system for saidr compressing means and connected thereto to supply lubricating and coolingoil thereto, said inlet system including unloading means for unloading the compressing means, said receiver system including a separator means which receives air and oil mixture discharged from said discharge outlet of said compressing means for separating the oil and air of the miXture,-said separator means having an inlet for the mixture, an outlet means for the'air and an outlet means for the oil for returning it to said compressing means, a receiver'- system venting unloading means connected to said separator air outlet means, said ref ceiver system including a 'serviceline leading therefrom and connected to said separator air outlet means, a check valve in the service line for preventing venting of said line upon opening of said receiver system venting unloading means, and control means connected to both of said unloading means for actuating them simultaneously, said control means comprising a pressure line connected t0 said service line and to pressure-type actuating means for both of said unloading means.

References Cited by the Examiner UNITED STATES PATENTS 1,863,845 6/32 Halvorsen 230-26 2,221,789 11/40 Ferguson 230--26 2,516,291 7/50 Bartholomew 230-26 2,646,205 7/ 53 Munch Af Rosenschold 230'-24 2,730,296 1/56 Hartwell 230-24 2,739,758 3/56 Lamberton 230-207 2,894,677 7/59 Nash 230-210 3,072,319 1/63 Cox et al. 230-207 3,072,320 1/63 Cox et al. 230-207 20 LAURENCE v. EFNE'R, Primary Examiner. 

1. A ROTARY COMPRESSOR COMPRISING LOW-PRESSURE AND HIGH-PRESSURE STAGES HAVING AIR COMPRISING ROTORS, A PRESSURE LUBRICATING-COOLING SYSTEM FOR SAID STAGES AND CONNECTED THERETO FOR SUPPLYING THERETO, AN INLET VALVE CONTROLLING THE INLET OF AIR TO BE COMPRESSED INTO SAID LOW-PRESSURE STAGE, AN AIR AND OIL RECEIVER SYSTEM CONNECTED TO THE DISCHARGE OF SAID HIGH-PRESSURE STAGE FOR RECEIVING THE OIL AND AIR MIXTURE DISCHARGED THEREBY, SAID RECEIVER SYSTEM INCLUDING SEPARATOR MEANS FOR SEPARATING THE OIL AND AIR OF MIXTURE, SAID SEPARATOR MEAN HAVING AN INLET FOR THE MIXTURE, AN OUTLET MEANS FOR THE AIR AND AN OUTLET MEANS FOR THE OIL FOR RETURNING IT TO SAID STAGES A VENTING UNLOADING VALVE CONNECTED TO SAID SEPARATOR AIR OUTLET MEANS OF THE RECEIVING SYSTEM, SAID RECEIVER SYSTEM INCLUDING A SERVICE LINE LEADING THEREFROM AND CONNECTED TO SAID SEPARATOR AIR OUTLET MEANS THEREOF, A CHECK VALVE IN THE SERVICE LINE FOR PREVENTING VENTING OF SAID LINE UPON OPENING OF SAID VENTING UNLOADING VALVE IN THE RECEIVER SYSTEM, AND CONTROL MEANS CONNECTED TO BOTH OF SAID VALVES FOR CLOSING THE INLET VALVE AND OPENING THE VENTING UNLOADING VALVE TO FREELY UNLOAD THE COMPRESSOR, SAID CONTROL MEANS COMPRISING A PRESSURE LINE CONNECTED TO SAID SERVICE LINE AND TO SAID INLET VALVE FOR ACTUATING IT TO CLOSE SAID INLET VALVE WHEN PRESSURE IN THE SERVICE LINE REACHES A SELECTED UPPER LIMIT AND THEREBY TO UNLOAD THE INLET SIDE OF THE COMPRESSOR. 